The field of clinical chemistry is concerned with the detection and quantification of various substances in body fluids. Included among those substances which can be determined are cholesterol and glucose, urea, as well as cations such as calcium and potassium which are found in various body fluids such as urine and blood.
One of the most frequently used analytical devices in clinical chemistry is the test strip which is contacted with the body fluid to be tested. Various reagents incorporated into the test strip react with the analyte to be determined in the body fluid to provide a detectable signal which is typically a change in color. These color changes are measured either visually or, where greater accuracy is required, spectrophotometrically. The detected signal is correlated to a standard to thereby give a value for the amount of analyte in the sample.
Clinical analysis of the type described above, especially when automated systems are used, must necessarily be extremely accurate to ensure that the measurement taken is valid. Control reagents are used to verify this accuracy by determining that the device is giving the correct response.
A control reagent is a specimen or solution which is analyzed solely for quality control purposes and is not used for calibration. A suitable control reagent should be stable and available in aliquots or vials so that it can be analyzed periodically over a long time. There should be little or no aliquot-to-aliquot or vial-to-vial variation so that differences between repeated measurements can be attributed to the analytical method alone.
Modified human serum known in the art as "control serum" is one type of control material. One of the requisites of a control material is stability. Control materials based upon serum, however, are inherently unstable due to the various components contained therein. In addition, sera will vary from source to source thereby rendering unpredictable the reproducibility of the results of using control serum from different lots. Control reagents, with which the present invention is concerned, are control materials which are not based on, and do not contain, serum of any type.
U.S. Pat. No. 3,920,580 discloses that control reagents for glucose determinations can be prepared without any serum or components thereof by incorporating an antidiffusing agent into a glucose/water solution. The antidiffusing agents disclosed in this patent include polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, dextran and bovine serum albumin.
U.S. Pat. No. 5,028,542 discloses a glucose control reagent comprising a predetermined amount of glucose, water and polystyrenesulfonate or a soluble salt thereof.
These prior art control reagents are somewhat limited in that their stability, compatibility with the tetrazolium salt indicators used in certain test strips, and surface tension are all lower than that of serum. We have discovered a particular class of polymers for use in these control reagents which enhance the solubility of tetrazolium salt indicators and thereby improve the performance of the control reagent.